In order to meet the request that semiconductor devices are made finer and caused to have higher functions, the wiring width of power supply lines arranged in the entire area of the main faces of their semiconductor chips (semiconductor elements) or the interval between signal lines arranged therein has been becoming narrower. For this reason, the impedance thereof increases or signals between signal lines of different nodes interfere with each other so as to cause hindrance to the exhibition of sufficient performances for the operation speed of the semiconductor chips, the margin of the operating voltage thereof, the resistance thereof against damage by electrostatic discharge, and others. In order to solve these problems, for example, in JP-A-55-111151 and JP-A-2002-261233, package structures wherein semiconductor elements are laminated are suggested.
As a material used to stick semiconductor elements to a substrate or the like, the following examples are suggested: an example wherein a thermosetting paste resin is used (see, for example, JP-A-2002-179769); and examples wherein an adhesive sheet composed of a thermoplastic resin and a thermosetting resin is used (see, for example, JP-A-2000-104040 and JP-A-2002-261233).
In conventional processes for producing a semiconductor device, an adhesive sheet or an adhesive is used to adhere semiconductor elements onto a substrate, a lead frame or semiconductor elements. The adhesion is performed by attaching the semiconductor elements to the substrate or the like under pressure (die attaching) and then curing the adhesive sheet or the like in a heating step. In this production method, wire bonding is performed in order to electrically bond the semiconductor element and the substrate each other, and then the semiconductor element is molded with a sealing resin and post-cured to seal the element with the sealing resin.
However, when the wire bonding is performed, the semiconductor elements on the substrate or the like are shifted by ultrasonic vibration or heating. Conventionally, therefore, it is necessary to perform a heating step before the wire bonding so as to heat and cure the thermosetting paste resin or thermosetting adhesive sheet, thereby sticking/fixing the semiconductor elements so as not to be shifted.
An adhesive sheet made of a thermoplastic resin or an adhesive sheet composed of a thermosetting resin and a thermoplastic resin is required to undergo a heating step after die attaching and before wire bonding in order to ensure adhesive force thereof onto an object which is to be stuck with the sheet, or improve the wettability thereof onto the object.
However, there is caused a problem that volatile gas is generated from the adhesive sheet or the like by the heating thereof which is performed before wire bonding. The volatile gas contaminates bonding pads. Thus, no wire bonding will be able to be carried out in many cases.
By heating and curing the adhesive sheet or the like, curing, shrinking or the like is caused in the adhesive sheet or the like. With this, stress is generated so as to result in a problem that a warpage is generated in the lead frame or the substrate stuck on the sheet (as well as the semiconductor elements). Additionally, a problem that a crack is generated in the semiconductor elements on the basis of the stress is caused in a wire bonding step. In recent years, the thickness of semiconductor elements has been made smaller from a conventional thickness of about 200 μm to a smaller value, in particular, to a thickness of 100 μm or less as the semiconductor elements have been made thinner and smaller. Considering this situation, the problems about the warpage of the substrate or the like or the crack in the semiconductor elements are more serious. Thus, it is increasingly becoming important to solve the problems.    Patent Document 1: Japanese Unexamined Patent Publication S55-111151    Patent Document 2: Japanese Unexamined Patent Publication 2002-261233    Patent Document 3: Japanese Unexamined Patent Publication 2002-179769    Patent Document 4: Japanese Unexamined Patent Publication 2000-104040